Description: (Applicant's Description) The goals of the Immunology program are: 1. To provide a supportive environment to facilitate interactions among investigators who are interested in a basic understanding of the immune system and immune responses. This encompasses not only the development and differentiation of immunologically related cells, but also the regulatory processes that control the types of immunological effector activities that develop and the nature of those effector activities. 2. To promote collaborative research that relates directly to an understanding of the role of the immune system and the immune response in the control of cancer. Only some immunological effector activities appear to be relevant for the control of tumors, and the development of one type of response often precludes the development of others. It is important to understand the nature of the antigens recognized on tumor cells both for their utility as therapeutic agents and in order to determine why immune responses to them are so frequently ineffective in controlling tumor growth. 3. To provide a sound scientific basis for the development of translational research and clinical programs in tumor immunotherapy and bone marrow transplantation. It is increasingly clear that the immune response to cancer cells will provide important new therapeutic modalities, and that their successful development and exploitation requires significantly greater understanding of how immune responses are controlled. In addition, as bone marrow transplantation is increasingly utilized as a therapy for cancers, it is important to understand the immunological ramifications of this procedure. 4. To provide an understanding of the normal development and differentiation pathways followed by lymphoid cells may provide important insights in to the control of cancers of lymphoid origin. Accordingly, this program is divided into 3 subprograms: 1) Definition of antigens and the nature of antigen recognition; 2) Differentiation and activation of lymphocytes; and 3) Regulation of immune effector activities.